Pump dispensers having a pump mounted on a container are widely used for dispensing fluid products (liquids, creams, pastes) such as medicaments, bathroom products and cosmetics. Generally, a dispenser comprises a container for the product and a pump module mounted on the container at an opening thereof. The pump module comprises a pump body defining or incorporating a pump chamber, with a pump chamber inlet for the flow of product from the container into the pump chamber through an inlet valve. A pump actuator such as a reciprocable plunger is operable in a pumping stroke relative to the pump body to vary the volume of the pump chamber for dispensing the product through a discharge channel, often via an outlet valve, on depression of the plunger and for re-filling of the pump chamber through the inlet valve as the plunger rises, usually driven by a restoring spring. Often the plunger carries a piston which operates in a cylinder of the pump body, but alternatives exist.
Conventionally the container is upright with the pump on top, the actuating member such as a plunger projecting upwardly. So, for convenience the expressions “top”, “upper” etc. are used herein to refer to the conventionally-corresponding directions and positions (i.e. the extending directions of a plunger, the direction towards the pump rather than towards the closed end of the container space) and “bottom”, “downwards” etc. analogously refer to the opposite direction/position. Usually this is in fact the orientation, and is preferred herein, but should not be regarded as strictly limiting.
Certain of the present proposals are especially relevant for dispensers of the “airless” type in which the internal product chamber volume of the container reduces as product is dispensed, so that remaining product is not exposed to air. Such dispensers use containers with a follower piston which moves up the container behind the mass of product as its volume progressively decreases, collapsible containers or collapsible container liners. They are used when the fluid product is sensitive to oxidation or to airborne contamination, or should be kept clean for any other reason. These dispensers generally do not use a dip tube extending down into the product from the pump inlet; product enters the pump inlet directly from the container interior space.
Some flowable materials are hard to pump because they do not flow readily. These include certain greases, ointments and other “fluids” that are not naturally self-levelling. One frequent characteristic feature of these products is their plastic nature, exhibiting a definite yield stress. Under low or zero shear they retain their shape and do not flow or level at all. These properties are desirable e.g. for ointments which should not flow away from an application site. However they cause problems in the operation of pumps which rely on modest suction (usually from a pump spring) to fill (prime) the pump chamber through the inlet. The problems are exacerbated by the impossibility of filling the containers always to exactly the same level. When a product is already difficult to prime, a slight drop in level below the inlet can make it impossible. Accordingly, there is a range of products which is not supplied in pump dispensers but instead packaged in tubs from which the lid must be removed and the product taken out with fingers or a spatula. This is messy, tends to contaminate the tub contents and there is no uniform dosing. It would be much better to dispense a controlled, meter dose as with a pump.
The state of the art includes proposals for pump dispensers of the airless type such as EP-A-1015341, EP-A-2153908, EP-A-2095882, EP-A-2353727 and EP-A-1629900 in which the bottom of the pump module dips into the top of the product, displacing product upwardly to fill the pump chamber and/or to displace air out from the package before sealing. However, these dispenser types may not be effective with very thick products.
In the present invention we provide several proposals for new features of pump dispensers which can improve their performance with thick, viscous, pasty or waxy products. In embodiments, our proposals are for use with products which have scarcely been pumped successfully before, such as ointments displaying a yield stress or shear-thinning/pseudoplastic properties, which typically are based on a mix of solid and liquid hydrocarbons including microcrystalline waxes for structuring. Also, for general flowable materials showing a viscosity of 30, 40 or even 50 Pa·s or more at room temperature and pressure. However, the new proposals also offer conveniences with less demanding products, as will be understood from the description which follows.